Place beef bones, carrots, leek, onion, and garlic on a roasting pan or rimmed baking sheet and roast for 20 minutes. Toss the contents of the pan and continue to roast until deeply browned, about 20 minutes more.

Fill a large stockpot with 12 cups of water (preferably filtered) . Add celery, bay leaves, peppercorns, and vinegar. Scrape the roasted bones and vegetables into the pot along with any juices. Add more water if necessary to cover bones and vegetables.

Cover the pot and bring to a gentle boil. Reduce heat to a very low simmer and cook with lid slightly ajar, skimming foam and excess fat occasionally, for at least 8 but up to 24 hours on the stovetop. (Do not leave on stovetop unattended, simply cool and continue simmering the next day.) The longer you simmer it, the better your broth will be. Add more water if necessary to ensure bones and vegetables are fully submerged. Alternately, you can cook the broth in a slow cooker on low for the same amount of time.

Remove the pot from the heat and let cool slightly. Strain broth using a fine-mesh sieve and discard bones and vegetables. Let continue to cool until barely warm, then refrigerate in smaller containers overnight. Remove solidified fat from the top of the chilled broth.

Do Ahead:
Broth can be stored for up to 5 days in the refrigerator and up to 6 months in the freezer.

Hints & Tips:
The longer you cook this nourishing broth, the more savory and concentrated it will become. Roasting the bones and vegetables beforehand will add even more flavor and richness. Season with salt and sip this restorative broth on its own, use it as a cooking liquid for grains or legumes, or deploy it as a base for sauces and soups like hearty, healthy Detox Pho.